1. Field of the Invention
The present invention relates to a water-based ink set for ink-jet recording suitable for reducing graininess in a low-density printed part, for extending a color reproduction range, for improving light fastness and for improving gas resistance. The present invention also relates to an ink-jet recording method using this water-based ink set for ink-jet recording.
2. Description of the Related Art
When a color image is formed by use of an ink-jet recording method, a three-color ink set has been generally used which is composed of a yellow ink (Y), a magenta ink (M) and a cyan ink (C). Alternatively, a four-color ink set has also been used in which a black ink (K) is further added to the three-color ink set.
Generally, in an ink-jet recording method, the gradation of an image is controlled by adjusting the density of dots formed by ejecting ink onto a recording material. However, when the gradation is controlled by such a method, the dot density decreases in a low-density printed part. Relative to this, the individual dots become easily discernable to the eye, thereby causing a problem that the image is grainy.
In view of the above, a method has been proposed in which two or more inks are employed as cyan ink (see Japanese Patent Application Laid-Open No. H01-95093). In this method, these inks have different dye concentrations and are composed of different kinds of dyes. In addition, a dye which is excellent in vividness but inferior in light fastness is employed in a dark color ink, and a dye which is excellent in light fastness but inferior in vividness is employed in a light color ink. Moreover, a similar method has been proposed for magenta ink (see Japanese Patent Application Laid-Open No. H02-127482). According to these methods, graininess can be improved, but a problem remains that a color reproduction range cannot be extended. Further, when dye ink is employed, color fading first occurs in a low-density printed part, and only the low-density printed part becomes whitish. Thus, the color tone of the image is changed, and the density difference of the image becomes excessively large to cause the overall image balance to be lost. Therefore, gas resistance, particularly ozone resistance, of a printed part is important.
Generally, in a three-color ink set composed of yellow, magenta and cyan inks, and also in a four-color ink set in which a black ink is added to the three-color ink set, red color is developed by use of the magenta ink and the yellow ink. When these two inks are used to develop red color as above, a problem arises that sharp printing quality and vivid colors are difficult to achieve due to a landing error of superposition.